1. Field of the Invention
This invention relates to laminates used in glazing applications. This invention particularly relates to a process for improving adhesion between layers in glazing laminates.
2. Description of the Related Art
Polyethylene terephtalate (PET) film can be used as a laminate layer in laminated glazing products. In such laminate products, the PET layer can be in contact with other polymeric layers of the laminate. Such commercial laminates as SENTRYGLAST™, and SPALLSHIELD™ products, which are laminate combinations of PVB and polyvinyl butyral available from DuPont, are examples. Imbedded film applications (for example, MET is PET imbedded between layers of PVB) are still other examples.
Glass/plastic laminates (that is, laminates having glass on one outer side and a hard plastic or hardcoated plastic on the other outer side) made using PVB interlayer with a PET film outer layer can be quite compressible because of the soft underlying PVB interlayer. Such laminates are vulnerable to gouges and impressions when hard objects impact them or are pressed against them for some time. If the impressions are deep, they can become permanent and this mars the appearance of glazing using such glass plastic laminates.
Harder interlayers would make the plastic side of glass/plastic laminates harder and less prone to gouging and pressure-induced impressions. However, use of such harder interlayers has been prevented by the lack of a sufficiently adherable PET film. For example, PET film treated by electrical discharge, various plasma treatments, or flame treatment does not adhere well to harder interlayers such as ionoplast sheeting, for example DuPont's SENTRYGLAS™-PLUS (SGP) interlayer.
To obtain the PET laminates such as those described hereinabove, it can be necessary to flame treat the PET layer under controlled conditions to enhance its adhesion to PVB on one side and to a hardcoat such as a polysiloxane abrasion resistant coating (PARC) on the other side. The adhesion strength, as measured by the 90-degree angle peel test, averages about 10 lb/inch. The flame treatment is done in a separate operation from the PET film casting. U.S. Pat. No. 5,415,942 describes a hydroxy-acrylic hydrosol primer coating that, when applied to one side of a PET film, greatly improves adhesion of the PARC. However it does not improve adhesion of the PET to the PVB interlayer. Therefore the primed film still needs to be flame treated on the non-primed side.
Also, the adhesion between PVB and ionoplast resins is poor, and so laminates having these two polymer interlayers in contact are not viable for many of the applications in which these interlayer materials find use.
It can be desirable to have a primer that can improve adhesion of PET to PVB and/or ionoplast resins, and also improve adhesion between PVB and ionoplast resins.